1914] The Ottawa Naturalist. 63 



Transpiration. It has been a readily attained and rather 

 generally accepted view that the abscission of leaves may be 

 induced by disturbances in the water relations. The promptness 

 with which many desert plants lose their foliage with approach- 

 ing drought and their readiness to refoliation, even though 

 stimulated thereto by such moisture as might be absorbed by 

 their branches from rain (Lloyd, 28), as I have shown experi- 

 mentally to be the case in Fouquieria; the dropping of leaves by 

 houseplants on too meagre or too generous watering, both go to 

 show that, directly or indirectly, such conditions may induce 

 abscission. The early shedding of tendrils in Ampelopsis, above 

 cited, may have been due to excessive transpiration. That 

 merely reduction of water content of the leaf is, however, in- 

 adequate, in itself, to produce the result is shown by the fact 

 that daily "incipient drying" and actual wilting, which we know 

 from observation (Lloyd, 29), (Livingston and Brown, 30) to 

 occur, is not followed by any such result. Desiring to produce 

 abscission by reducting the water supply to organs known to 

 be able readily to be caused to shed, I did the following experi- 

 ments: A large sector (90°) of tissue was removed in a dozen 

 cases from the stem below the insertion of the tendril in 

 Atnpelopsis Virginiana, and it was found impossible' to induce 

 abscission, although it will occur in cut branches in 36 or 48 

 hoiirs in a moist chamber, without measureable loss of turgor, 

 though doubtless there was some. The wounds healed, and they 

 were later examined microscopicalh^ and all the vascular supply 

 to the tendrils was found to be extirpated for a distance of 

 5 to 10 mm. The water supply must then have passed around 

 the wound, travelling laterally below and above it, yet either 

 without the least prejudice to its movement or quantity, which 

 is difficult to believe, or, if such prejudice obtained, without 

 inducing abscission. 



For some time I held the view that the peculiar anatomical 

 relation in. the flowering branch of the cotton was responsible 

 for much of the boll-shedding. The view had been expressed 

 that the shedding of fruit by orchard trees, said more often to 

 occur near the ends of the branches, is due to the more favour- 

 able position of the proximal, since these are nearer the source 

 of supplies.^" The occurrence of the vascular tissue in an organ 

 of limited secondary thickening (the flower-stalk) alongside that 

 in one of unlimited secondary thickening, namely, the function- 

 ally chief axis, seemed to supph^ a possibility for an increasing 

 prejudice to the water supply of the boll as growth of the whole 



'"Sorauer, P. Abwerfen der Frflchte. Handbuch der Pflanzen- 

 krankheiten. 



